This invention relates to a method for recovering energy raw materials from a subterranean formation by the introduction of cryogenic liquids containing oxygen into the formation.
Recovery of energy raw materials from subterranean formations is done by several methods such as fracturing the formation, in-situ combustion, and thermal displacement. The invention of the in-situ combustion method for petroleum recovery by F. A. Howard in 1923, did not yield substantial recoveries until recently due to control problems and the unpredictability of the method. This in-situ combustion method produces sufficient heat within a petroleum reservoir which, by means of partial combustion of the oil residues in the petroleum reservoir, enable the recovery of the remaining oil. The important processes contributing to petroleum displacement are (1) viscosity reduction by means of heat, distillation and cracking, (2) sweeping out of the oil with hot water, and (3) extraction of the oil by means of miscible products. This is similar to the method specified in U.S. Pat. No. 3,026,935. There are benefits to the use of higher partial pressures of oxygen in injected combustion sustaining fluid in that a miscible carbon dioxide product would be formed and the mix would have greater reactivity. The amount of combustion heat released for example in a reaction between oxygen and organic fuels is on average 3,000 kcal. per Kg oxygen.
Oxygen has draw backs as a gas when used with energy raw materials and steel. Its reactivity in higher purities can cause fires and explosions. The handling of compressed oxygen flowing through piping systems requires special precautions which have been developed. Such precautions include the use of large inner surfaces in relation to volume, appropriate geometry to prevent local temperature peaks, and lower purity oxygen content, i.e. at less than 95% steel can be ignited but combustion is not self-sustaining. This leads to a need for obtaining the benefits of high partial pressure of oxygen in in-situ combustion without the foregoing drawbacks.
The reactivity of and associated danger of oxygen in a cryogenic liquid state is far less and its use is increasing. There are requirements due to the cryogenic temperatures. This is well understood and has been reduced to practice for decades, and amounts to the use of nickel alloys, aluminum, and certain design features, Within a petroleum formation, the channelling and vaporization expansion of the cryogenic fluid fractures the formation. The gaseous product of this volatilization causes a miscible and/or non-miscible displacement of the oil driving it from an injection borehole to a production borehole in a flood pattern arrangement. The characteristics of cryogenic liquid nitrogen are known in a variety of formations as are the combustion characteristics of oxygen containing gases. The physical properties of a cryogenic liquid containing oxygen would be similar to cryogenic liquid oxygen. The combined effect would be predictable to an extent based on information on specific formation experience with cryogenic liquid nitrogen and oxygen containing gas relative to introduction into said formation of a cryogenic liquid containing oxygen.
According to U.S. Pat. No. 4,042,026, the most dangerous point along the oxygen flow path is the borehole. This danger could be lessened or eliminated by several means. The very nature of a cryogenic liquid containing oxygen lessens said danger. Also, a cryogenic liquid with lesser concentration of oxygen or no oxygen may be injected as a pretreatment. There are many gases and liquids which may be injected into the borehole and which, through reaction or displacement, lessen said danger. Another means would be through the limited injection of an oxygen containing gas, causing a limited in-situ burn in the borehole and adjacent energy raw material containing formation.
It is therefore the objective of this invention to recover energy raw materials namely, petroleum hydrocarbons, including shale oil, heavy oil, natural gas, and oil from depleted wells or unobtainable by other means more efficiently in appropriate substerranean formations, preferably using conventional equipment used in boreholes for the recovery of energy raw materials such as petroleum hydrocarbons.